Thanks for the feedback! While I disagree that the pricing is insane, you and other commenters here made me realize that maybe we presented it badly.
TalkJS is 10 cents per conversation per month, plus a fixed monthly fee.
I think our mistake has been that we made the fixed monthly fee also include a small number of conversations, which is where all the confusion comes from. It makes it seem like a single conversation costs $2.
The idea behind our pricing is that with a small app you can go live with TalkJS with pretty much the fixed monthly $49 or $249. Once your traffic increases, the price-per-conversation takes over and it's really just 10 cents per conversation, period.
Note that we also offer large bulk discounts for large sites - do get in touch!
Also, I forgot to answer your question. Indeed the 10 cents is per conversation. A conversation can last as long as you want and is only counted once (we charge for a conversation when the first message is sent in it).